In: Physics
Two cars start from rest at a red stop light. When the light turns green, both cars accelerate forward. The blue car accelerates uniformly at a rate of 3.6 m/s2 for 4.4 seconds. It then continues at a constant speed for 8.1 seconds, before applying the brakes such that the car
For blue car ..
a) for initial acceleration
a = 3.6 m/sec
t = 4.4 sec
u = 0
so.. distance moved = s = ut + 0.5*a*t^2 = 0 + 0.5*3.6*4.4^2 =
34.848 m
speed after accelerationg = v = u + at = 0 + 3.6 * 4.4 = 15.84
m/sec
b) now for constant speed
speed = 15.84 m/sec
time = 8.1 sec
so. distance moved = 15.84 * 8.1 = 128.304 m
c) for retardation..
disance moved = s= 206.36 - 128.304 - 34.848 = 43.208 m
intial speed = u = 15.84 m/sec
final speed = v = 0
let the accletiaontion be a
so.. v^2 = u^2 + 2*a*s
0 = 15.84 ^2 + 2*a*43.208
so.. acceletiaon =a = - 2.90346 m/sec2
time of travel while retarding = ( v - u ) / a = ( 0 - 15.84) / (-
2.90346) = 5.45556 secs
4) so the acceletiaon of the blue car once the brake are applied =
- 2.90346 m/sec2
5) so.. total time of travel for blue car = 5.45556 + 8.1 + 4.4 =
17.95556 secs..
6) for yellow.. let the acceeltaion be a ..
time t = 17.95556 secs
intial speed , u = 0
distance moved = s = 206.36 m
s = ut + 0.5*a*t^2
206.36 = 0 + 0.5 * a * 17.95556^2
so.. acceletiaon a = 1.28 m/sec2